Two XML documents can contain identical information yet differ in terms of raw bits. The documents merely need to differ in whitespace. There are many other ways the documents can differ, such as the order of attributes. This makes comparing XML documents difficult. Canonical XML addresses this issue by defining a process in which an XML document can be transformed such that two logically identical documents are in fact identical if you use a tool such as "diff" to compare them.
EditHint: Difference between this topic and XmlIsCanonical needs to be clarified.
The author of XmlIsCanonical may not be aware of this page.